1. FIELD OF THE INVENTION
This invention pertains generally to semiconductors, and more particularly to photodiodes and methods of fabricating the same.
2. DESCRIPTION OF THE RELATED ART
In order to maximize the advantage of the high sensitivity of photodiodes to light, it is important that the diodes exhibit very low electrical noise when coupled to electronic circuitry. Typical applications include solid state detectors for tomographical instruments, security scanners, and other applications in which very low light levels must be measured accurately.
The parameters which most affect the ability of a detector to measure low light levels are the responsivity to the particular wavelength of light, and the area, the capacitance and the shunt resistance of the diode. Most photodiodes have good sensitivity at their operating wavelengths, but the other parameters are difficult to optimize with photodiodes of the prior art. The optimum parameters are large area, low capacitance and high shunt resistance. Since capacitance is proportional to area, increasing the area of prior art devices has also increased the capacitance. There have been attempts to reduce the capacitance by increasing the resistivity of the starting material, but this has resulted in an undesired decrease in the shunt resistance. The use of a starting material of high resistivity also has the disadvantages of high cost, difficult processing due to the susceptibility of high resistivity materials to contamination, and a large amount of edge damage during dicing of wafers which tends to reduce the shunt resistance.
It is in general an object of the invention to provide a new and improved photodiode structure and method of manufacture which overcome the foregoing and other disadvantages of photodiodes heretofore provided.
Another object of the invention is to provide a photodiode of the above character which has a relatively large equivalent photosensitive area, a relatively low capacitance and a relatively high shunt resistance.